Method of precision casting



Aug. 26, 1958 I M. F. BROWNE METHOD OF PRECISION CASTING 4 Sheets-Sheet1 Filed May 14, 1953 lITilll INVENTOR. MERviN F'BROWME 6, 1958 M. F.BROWNE 2,848,773

METHOD OF PRECISION CASTING Filed May 14, 1953 4 Sheets-Sheet 2 CURING50 OVEN /2 L :f ';l-.-= I G) (5) IN VEN TOR.

F775 MERViN F'BRowNE Aug. 26, 1958 M. F. BROWNE METHOD OF PRECISIONCASTING 4 Sheets-Sheet 3 Filed May 14, 1953 INVENTOR. MER vI'N F-BRo WNEAug. 26, 1958 M. F. BROWNE 2,843,773

METHOD OF PRECISION CASTING Filed May 14, 1953 4 Sheets-Sheet 4 IIIIIHT! Z U iNVENTOR.

MERVJ'N F-BRowNE Zfiififlii Patented Aug. 26, 1958 ice gash

asasms ivmrnon or PRECISIUN cAsrnso Mervin F. Browne, Toledo, @hio,assignor, by mesne assignments, to Allied Chemical Corporation, acorporation of New York Application May 14, 1953, Serial No. 355,125

6 Claims. (till. 22-195) The present invention relates to precisioncasting methods and more particularly to a method for precision castingmetals utilizing rigid, self-supporting, resin-bound sand molds of highpermeability and high finish.

In general foundry practice metals are cast in molds made of moist orgreen sand. In ordinary sand molding the sand ismerely mixed with a clayand dampened so as to be readily packed, rammed or blown into shape overa pattern. Since the wet sand has very low strength, a large quantity ofthe sand is packed or rammed about the pattern in a heavy frame or flaskusually made of metal. This method produces metal castings having arough finish and of only approximate dimensions since the Wet sandmixture is easily eroded or displaced by the molten metal. Considerablemachining and finishing of the castings is necessary to produce metalparts of good finish and accurate dimensions. Rather coarse sand isrequired in this method in order to permit escape of gases from theheavy mass of sand surrounding the molten metal.

Another process known as the C process or Croning process utilizes thinresin bonded molds or shells made from a fine powdery mixture of a dry,very fine sand and a dry, fine powdery resin binder composed of amixture of spray-dried phenol-formaldehyde resin and hexamethylenetetramine. In this process the shell mold can be made of much finer sandthan ordinary green sand molding because vapors can escape because ofthe thinness of the shell and the porous nature of the shot or gravelbacking. In this shell molding method the fine, dry sandresin mixture isdumped onto a heated metal pattern and allowed to stand until a thincrust forms by melting of the resin binder. The excess dry sand-resinmixture is then poured OE and the thin crust rendered hard anddimensionally stable by continued heating in contact with the hotpattern to cure the resin to the thermoset condition. The thin shell ormold is then stripped from the pattern, assembled, clamped together andsupported by metal shot, gravel, or other supporting means. Finally,molten metal is then poured into the shell mold and allowed to solidify.The resultant casting possesses a very smooth finish due to the use ofvery fine sand and firm binding of surface grains. When the shell isproperly and carefully made, and adequately supported, the castings areaccurate as to dimension and very little machining or finishing isnecessary.

The described C process of shell molding has not enjoyed as Wide anapplication as would appear justified by casting quality because ofseveral fundamental and inherent disadvantages. Firstly, since themanner of forming the shell is dependent on a sintering or melting of adry resin which will later cure to the thermoset condition, the methodis virtually limited to the use of the phenolic resin and the hexacuring agent. Other thermosetting resins such as urea-formaldehyde resincure too rapidly, alkyd resins cure too slowly and both do not melt orfiow sufficiently to ensure good sand binding action. Such resins havenot formed satisfactory shells in contact with a heated pattern.Secondly, the light metals, particularly magnesium, can not be castsatisfacton'ly in phenolic-bonded shell molds due to the poorcollapsibility characteristics of the phenolic resins. Thirdly, the drysand-resin mixture raises a dusting problem that is only partiallyovercome by special handling equipment. Fourthly, the dry sand-resinmixture is sensitive to moisture, producing weaker shells after standing for any length of time in contact with a humid atmosphere. Incommercial use this means fresh daily preparation of the sand-resinmixture for best results. Fifthly, in order to obtain adequate bondingof the sand grains a very high resin-to-sand ratio is required.

A sixth disadvantage is that production capacity is strictly limited bythe dwell time necessary for sintering and cure of the resin while incontact with the metal pattern. Production with each patternconsequently is strictly limited by the resin curing characteristics sothat multiple patterns and their accompanying heavy dump boxes, sandhandling equipment, etc. are required for high output. A seventhdisadvantage resides in the requirement of the process for massive andexpensive equipment of special design which is not, nor is itsusceptible of, general use in ordinary foundry practice. The dumpingboxes, special sand handling equipment and shotcleaning and handlingequipment are illustrative of the more expensive units required.Moreover, since the patterns must be of metal and fitted with specialheating devices, they tend to be very heavy and expensive, their costconstituting a substantial proportion of the total installation cost.Retooling for design changes is likewise a considerable element of cost.

An eighth disadvantage of the process is the properties or rather thephysical shape of the shell mold itself. The dump-box technique makes itextremely diificult to accurately control the thickness of the shell orits outer configuration. The thickness of the shell depends on a greatmany variables including dwell time, the weight of sand overburden onthe pattern, and on the maintenance of an even temperature over theentire surface of the pattern. In any case, the outer surface of themold is very rough and uneven. Warping troubles are encountered when thehot shells are removed from the pattern and especially when it isattempted to support the shell by its outer surfaces. The method islimited in the size of castings that may be produced because (1) theweight of the metal pattern becomes excessive (patterns up to 300 lbs.or more are not uncommon) and because (2) thin shells in larger sizesare very difficult to handle, assemble and support. Other disadvantagesexist, and although of lesser importance than those enumerated, in theaggregate they make for a costly and difiicult operation.

It is the principal object of this invention, therefore, to provide aprocess of precision casting of metals that is susceptible of generalapplication and utilizes standard foundry techniques and equipment.

A further object is to provide such a method which is applicable to allmetals and which makes possible the utilization of wet sand mixtures andinexpensive watersoluble or water-dispersible resinous binders.

Another object is to provide such a method which is capable of higherproduction rates at a lower cost and Without the disadvantages of knownsand molding methods. Still further objects will become apparent in thedescription which follows.

I have found that economical casting of metals with great precision andhard, rigid, self-supporting and highly permeable sand molds areeconomically produced by a method wherein molding sand or otherfinely-divided refractory molding material is mixed with an aqueoussolution of a water-dispersible or Water-soluble butheathardenablebinder to form a wet sand molding mixture which is thenmolded into a sand molding, or component part thereof, While in contactwith a reusable or removable'box-drier, thebox-drier and its adheringwet or green sand mold removed from the pattern, pattern box or otherenclosure and subjected to baking to heatharden the binder and drive ofia major share of the moisture, and finally the heat-hardened andself-supporting mold, or its components, separated from the drier andassembled. The box drier is of a unique type in that itdoes not functionin the shaping of any metalcontacting'surface of the mold, but rathershapes the exterior surface or surfaces thereof only so as toincorporate therein supporting and reinforcing means whereby there isproduced a strong, rigid and self-supporting sand mold which does notrequire racks, frames, shot-support, or clips or fasteners for assembly.A preferred embodiment utilizes integrally-molded interlocking legs orother means on the mold "exterior and integrally molded runners, sprues,etc. in the mold to permit vertical or horizontal assembly or stackingof a plurality of sand molds for simultaneous pouring.

The method of this invention has many advantages, the most importantbeing the production of castings accurate'to (3.003 inch or less andwith an exceptionally smooth surface requiring little machining orfinishing. Thewater and binder may be incorporated in the sand inconventional muller-type mixers now standard in the foundry industry;The method also makes the most efiicient use of binder by coating eachsand grain with a thin coating. The wet sand mix may be molded by anyconventional foundry technique such as ramming, bumpthickness of themold and eliminates warpage problems during cure and cooling. Mostimportantly, the drier completely eliminates dwell time in the patternor pat tern box and thus makes for maximum utilization of expensivepatterns and accompanying molding equipment. The drier also permits theuse of the high efficiency and high speed of electronic heating duringbaking. For this latter purpose the drier must be made of a suitable dielectric material such as wood, plaster, plastic, andthe like. Anespecially suitable material of construction for the drier is a mineralfiber filled or glass fiber filled alkyd molding compound.

In the practice of the method of this invention a moist mixture of finesand (about A. F. S. No. 100) and an aqueous dispersion or solution of awater-dispersible or -soluble binder, preferably a resinous binder, iscompacted and given its proper shape while in place on a novel-type ofbox-drier. This compacting and shaping may be performed by tamping thesand into a box or flask containing the box-drier or it may be done byblowing with a sand blowing machine of the type used in making cores.The latter procedure is much preferred because of the ease, speed andeconomy of operation.

The box-drier which makes the method of this invention practical is of anovel type, in the core-making art box-driers or trays are utilized tosupport odd-shaped cores which are not free-standing or self-supporting;The

surface of such driers are hollowed-out; so as to fit an outside surfaceof the core and support it during baking. Thus such a drier actuallycontacts surfaces of the core eventually to be exposed to molten metal.The driers utilized in this invention are quite difierent in that theynever function in the shaping or supporting of metalcontacting sandsurfaces, rather they shape and mold the outer surfaces only of the sandmold. T he drier molds the exterior surfaces of the sand mold intosmooth planar surfaces, into supporting bosses and legs and, if desired,into precision-fit interlocking means whereby the finished, cured sandmold canbe assembled and will support itself without backing or supportof any kind. By suitably designing the box-drier the finished sand moldscan be made to nest one within or against each other andto interlock soas to form a self-supporting multiple-mold assembly. it is not necessaryto design a special boxdrier for each article to be molded. A suitablerange of sizes of box-driers of standard design can be provided for theproduction of molds for a wide variety of articles or castings. Thus theexterior configuration of the sand mold can be standardized irrespectiveof the configuration of the interior metal-contacting surfaces. Whensuch a box-drier is utilized in a blowing machine, in many cases onlythe design of the blower head need be changed.

The drier, with its adhering mass of moist sand, is removed from themold box or flask, or from the blowerhead assembly, and placed in acuring oven to effect drying and/or curing of the binder. In this waythe expensive mold box or blower head is not tied up in dwell time butmay be utilized. to a maximum extent in the forming or blowingoperation.Wet sand molds can be produced at a rate of 100 to 350 or more an hour,for example, with a suitable core blowing machine. This is a rate ofproduction far beyond any of the so-called shell" molding processes.Breakage or damage to the wet sand molds is at a minimum.

The curing or baking of the sand molds may be performed in any way andwith any equipment conventionally used to bake cores. Gas or oil firedovens may be used although the preferred oven employs high frequency orelectronic radiation as a source of heat. The wet sand mix is ideal forthis type of heating for the resin binder is fully cured in a matter ofseconds. Continuous tunnel-like ovens can be used for maximum productionrates.

Once the resin binder is cured or the non-resinous binders dehydrated ordried out the sand mold is strong and not susceptible to damage inhandling. The sand mold may then be removed from the box-drier withoutfear of damage.

- The sand mold or component thereof made as just described is easilyassembled for pouring. For ordinary operations it is not necessary toglue, bind or otherwise fasten the various parts of the mold together.The precision-fitted outer surfaces of the mold permit vertical orhorizontal stacking'to form a multiple-mold assembly capable of pouringofl? in one step.

By this method single or multiple-cavity molds can be assembled intomultiple-mold assemblies. The gates, sprues'and runners can beincorporated in the sand mold itself to further simplify the assemblyand pouring steps. The method thus makes possible precision casting ofmetals at costs approaching those or ordinary foundry I ating costs. Themethod uses the inexpensive and readilyavailable Water-soluble orwater-dispersible resins binders such as urea, phenolic, melamine, andothers. Since the method permits the use of urea resin binders itsolvesthe problem of precision-casting of magnesium and aluminum andtheir alloys, and, moreover, makes possible the inclusion in the sandmix of the water-soluble inhibitors. needed for the casting of thesehighly-reactive light metals. Other advantages of the method willbecome. apparent in the more specific description to follow. Theinvention will now be more fully described with reference to thedrawings which demonstate the application of-the method to theproduction ofa simple ash-tray.

Of the drawings: v

Fig. l is a vertical section through a blowing machine assemblyincluding the blower head, a box-drier and supporting plate.

Fig. 2 is a plan view of the box-drier or tray shown in Fig. 1.

Fig. 3 is a front view of the box-drier of Fig. 2.

Fig. 4 is a perspective view, partially in section, of the box-drier ofFigs. 1 to 3 with freshly blown sand in position thereon.

Fig. 5 is a schematic view of a continuous mold curing machine withbox-driers and their adhering blown sand mold parts in position thereon.1

Fig. 6 is an exploded view of the box-drier with a cured sand moldcomponent of Fig. 4 partially lifted away.

Fig. 7 is an elevational view in detail of the blower head shown in Fig.1.

Fig. 8 is a plan view in detail of the blower head shown in Fig. 1.

Fig. 9 is a front elevation, partially in section, showing an assemblyof molds made by the blower-head assembly of Fig. 1.

Fig. 10 is an elevation in section of an individual ashtray made in themold assembly of Fig. 9.

Fig. 1 illustrates a blower-head assembly comprising a blower-head ll),a base-plate l1 and a box-drier or tray 12. The blower-head 16 ismovable in a vertical direction and fits tightly down on the drier 12forming a seal around the upstanding drier edge 13. Tie moist sandresinmixture is blown into the cavity thus defined through one or more smalltapered holes 14, 14 (only one of which is shown in dotted lines in Fig.l). The air escapes from the cavity through a number of similar exhaustholes 15, 15 (likewise only one of which is shown in dotted lines inFig. 1). Screening the exhaust holes materially reduces sand loss. Theplacement of the holes in the blower-head it) of Fig. l is merelyillustrative, since this is a matter of skill for the tool and diedesigner and usually requires slight modifications for each blower-headdesign.

In Fig. l the blower head 10 contains both a projecting male molding orshaping member 16 and recessive female molding or shaping member 17 inside-byside arrangement. Thus the lower head it is designed to formone-half of a two-cavity sand mold, the complete mold being formed byassembling twcsuch sections in mirror-image end-fcr-end fashion. theblower head it} functions as a pattern that forms all interior surfacesof the mold which eventually contact molten metal while the box-drier 22forms only the exterior mold surfaces. For the latter reason the designof the box-drier 12 does not have to be changed with w each blower-head,a satisfactory standard drier design of suitable size being capable ofuse in the blowing of molds for variegated-shaped articles. Thus thecost of the drier 12 for each molding production item is but a smallfraction of the total cost. It is obvious also that the blower head 15can contain a plurality of each of the shaping members 16, 17 so as toform a plural-cavity mold. The blower head 19 will be described ingreater detail in connection with Figs. 7 and 8.

The box-drier 12 is shown in greater detail in Figs. 2, 3 and 4. Theupper sand-contacting surfaces of the boxdrier 12 appear in detail inFig. 2. For example, the four corners 2-3, 2% are hollowed out to formrightangular depressions 2t, 22 of a novel stepwise design, the lefthand corners 21, 21 of the drier 12 having shallower central projectionsor legs 23, 23 and deeper side steps 24, 24 While the right-hand corners22, 22 have a mating stepwise leg design in which the central portion 25is deep and the side steps 26, 26 are shallower. As a result of this legdesign, which will be referred to in terms of the sand mold itself inconnection with Figs. 6 and 9, it is possible to fit vertically-stackedmolds together and lock them against rotation in the horizontal plane.

Also showing in the view of Fig. 2 are two rectangular in thisarrangement edge reinforcing sections 27, 27 whose purpose is toreinforce the long edge of the sand mold against war-page or breakageafter cure or baking of the mold. Also provided are two circularleg-forming depressions 28, 28 which form supporting bosses on the moldexterior. A circular depression 29 is provided for forming a massivesupporting boss on the exterior of the sand mold roughly correspondingto the bowl section of the ash-tray. The hole 30 is provided to define asprue hole in the final mold. Between the hole 3%? and the circulardepression 29 there may be provided a connecting passageway orgate-defining slot 31 to receive a corresponding projection on theblower head lltl. Through this latter arrangement, as will be more fullydescribed in connection with Figs. 6, 7 and 9, there is provided arunner-gate assembly for pouring off a vertical stack of two-cavitymolds.

in the front elevational view of Fig. 3 the details of the underside ofthe box-drier 12 are more readily seen. The four rectangular exteriorcorner legs 20, 20 are provided along with the two small conicalsupporting bosses 32, 32 (corresponding to 28, 28) a massive circularsupporting boss 33 corresponding to 29, and connected therewith anothercircular supporting boss 34 corresponding to 31'). In this manneradequate supporting surfaces are provided for the drier withoutexcessive weight and wastage of material. The underside of the box-drier12 could be solid if the Weight and material cost were no consideration.

In Fig. 4 there is shown the box-drier 12 with a freshly blown sand moldin place thereover. The top surface of the sand contains a circularraised male sand mold member a, a recessed circular female sand moldmember dtlb, and a sprue hole 42 and its connecting gate or channel 43.Also shown on the right-hand side is a small projecting peg orpositioning box 44 which is adapted to fit into a corresponding hole ina superimposed mold member such as is shown in the left-hand side at 45.When two mold members are matched, the

pegs 44, 44 and holes 45, 45 cooperate to align and position the moldsections and prevent slippage of one moldhalf relative to the other.Minor details visible in Fig. 4 are a plurality of circular humps 46, 46(only one being shown) for forming the cigaret-rests in the outer lip ofthe ash-tray and a circular decorative ring 47 in the face of the spruehole 42.

Referring now to Fig. 5, the freshly blown green sand mold of Fig. 4 iscured by placing it in a curing oven 50 which causes heat-setting of thebinder and drying of the cured mold. in an electronic heat oven themoisture is driven off before the sand temperature rises to curetemperature. Fig. 5 is a schematic representation of equipmentconventionally used for curing or baking cores. The boa-drier 12; filledwith sand is placed on the conveyor belt Si which carries it through thecuring oven Where electronic or other source of heat causes the cure.The box-drier 12 and its adhering cured sand mold is removed from theend of the conveyor and sand mold knocked out as shown in Fig. 6.

The bottom side of the sand mold is shown in Fig. 6 with greaterclarity. For example, the corner depressions 21, 22 of the drier formthe corresponding legs 6%, 61, respectively of the mold. Theinterlocking features of legs 60, 61 are shown more clearly, theprojection 62 on leg 61 being adapted to fit into the rectangular socket63 on a left-hand leg of another mold section. The small conical leg 64and the circular legs 65, 66 are formed by the corresponding parts 28,29 and 30 in the box-drier 12.

The blower head It? is shown with greater clarity in Figs. 7 and 8. Acircular projection 70 cooperates with the corresponding depression 30in the box-drier 12 to form a hole for a sprue. Between the projection70 and the male member 16 is a gate-forming projection or ridge '71which is suitably tapered to withstand how of ter, as compared to aconventional multi-part pattern and its accompanying box or flask forforming the molds in the conventional manner, of molding.

In Fig. 9 there is illustrated a vertical stack of molds, each composedof two half-molds as made in the blowerheadassembly of Fig. 1. Pairs ofthe cured mold sections 40, brought together in upside-down, end-forendfashion and then hooked together by positioning the pins 44, 44 in theholes 45, 45 to form individual assembled molds. Then the assembledmolds are stacked one 'on top of another by fitting the projection 62ofone mold into the rectangular socket 63 of another. In this way arigid mold assembly such as appears in Fig. 9 is built up. A heavyweight can be placed atop the stack to keep the individual mold sections40, 40 from separating when liquid metal is poured into the hole 42contained in the leg'65. The similar hole 42 at the bottom of the stackis blocked by resting the entire stack on dry molding sand or by a plugof molding clay (not shown). A funnel of molding clay (also not shown)can be atfixed to the top of 65 to facilitate pouring direct from theladle.v After the metal has been allowed to cool the burned out sand caneasily be shaken off. The individual ash trays are then cut off thesolidified runner. They are found to be of such a high finish as not torequire polishing or bufling. The finished ash-tray appears in Fig. 10.Lettering (not shown) disposed in the circular recess 80 is faithfullyand clearly reproduced. No faults occur about the cigaret rests 81, 81or about the raised ring 82. Dimensions and fine detail are reproducedto a tolerance of 0.01 to 0.001 inch or better.

Theinvention will now be more fully illustrated with reference toseveral specific examples illustrating various sand mixes and theirmanner of handling in the method of the invention. These examples areintended to be illustrative only and not as limiting the invention.

The ash-tray of the drawings is cast by the method described above. Ablower-head such as is shown in Figs. 1, ,6, 7 and 8 is cast in iron orsteel alloy and then polished to final dimensions. If desired, it may bechromium plated to give it a smooth, glass-like surface. A suitable,inexpensive mold for molding the tray-drier or box-drier of Figs. 1 to 4can be inexpensively cast in aluminum. Box-driers are molded of aglass-filled alkyd molding compound as Plaskon Type 440- or Plaskon Type444.

As one example, a sand mix is prepared using the following formulation:

A water-soluble, one stage, spray-dried phenolic resin in powder formand containing a curing catalyst.

The dry sand is mulled with the dry resin until a uniform mixture isobtained.v The water is then added to the resulting mixture and mullingcontinued until a uniform, damp mixture is obtained. The oleic acid ismixed with the kerosene and this mixture is added to the damp sand withcontinued mulling for several minutes. This mixture is utilized in acore blowing machine having an agitated hopper. The box-drier-blowerheadassembly utilized is shown in Fig.6. A uniformly compacted green sandmold component adhering to the box-drier is obtained. A suitable sandblowing machine can blow from to 350 or more of these half-mold sectionsper hour. The box-drier and its adhering green sand mold is placed in aradio-frequency or electronic core baking oven for cure. In a matter ofseveral minutes or less the mold has dried out and cured to a hardthermoset condition. When a plurality of these are assembled as shown inFig. 9, a multiple-cavity,plural-mold assembly air a. Cast iron,malleable iron, brass, steel, alubronze are cast in such molds.

have a high finish and are of accurate they require no polishing beforeuse. A sand mix adapted for blowing and to produce a ish, to preventmetal penetration and to permit e of higher melting steel alloys is asfollows:

Material: Lbs/wt. Silica sand-90 A. F. S 100.00 Silica flour-200 mesh1.0 Iron oxide-200 mesh 0.5 Fire clay-200 mesh 0.5 Dextrine powder-200mesh 1.0 Binder resin 1 4.0 Kerosene 0.2 Water 4.0 lsopropanol 0.25Kerosene 0.4 Oleic acid 0.01

1 Same as above.

As another example of this invention, magnesium and its alloys may becast in sand molds made as above using a sand mix as follows:

Material: Lbs/wt.

Silica sand-# A. F. S 100.0 Resin binder 1 4.0 Powdered sulfur 0.5 Boricacid 0.25 Potassium fluoborate 0.25 Dextrine powder 0.5 Kerosene 0.1

Powdered water-soluble urea-formaldehyde resin.

The above materials are mixed in a muller, then 3.0 lbs. of water, 0.5lb. of diethylene glycol, 0.40 lb. additional kerosene and 0.02 lb. ofoleic acid are added and mixing continued for several minutes. Theresultant damp sand mix is easily blown to form strong, firm green sandmolds using the box-drier of the drawings. When baked in a dielectricoven, the sand molds are hard and strong. They are easily removed fromthe box-drier without damage. if preferred, the interior surfaces of themold parts can be sprayed lightly with water or a water solution ofboric acid or an active fluorine-containing salt, a mixed solution ofsuch materials, or a mixture of boric acid and a suspension of sulfurbefore being placed in the oven for cure. An assembly mold prepared insuch a manner produces a sound, smooth casting of accurate dimensions.

In the molding process of the invention the water-dispersible bindersare utilized in amounts which vary quite widely depending on the binderagent employed. For example, the water-soluble binder resins areutilized in amounts ranging from 2 to 8% by weight based on the weightof sand. A preferred range is from 3 to 7% and most preferred from 3 to5.5%. These amounts of resin produced strong molds easily susceptible ofhandling in the cured state. Other conventional binders such as waterglues, clays, magnesium oxychloride, iron oxide, magnesium oxide,natural gums, and others are utilized in amounts, for example for clay,up to 10 to 20% or more. By the use of cementitious binders more or lesspermanent molds can be prepared by the process. The resinous binders,however, are most desirable for general application. Other conventionaladditives may be added in minor amounts to the resin-containing mixincluding core oils, other resins, starches, dextrines, cereal products,

The resultant humectants such as glycols and glycerol, silica fiour,fire clay, wood fiour, iron and other metal oxides, release agents suchas kerosene, fatt acids and other oily materials, and others.

It is preferred to utilize sand binder resins which are trulywater-soluble such as the urea-formaldehyde resins,melamine-formaldehyde resins, phenol-formaldehyde resins, acrylicresins, polyvinyl alcohol, water-soluble polyesters, styrene-maleicanhydride resins and their salts, carboxymethyl cellulose and its salts,vinyl alkyl ether polymers, and many others. The water-solublethermosetting resins of the ureaand phenol-aldehyde types are morepreferred because of their ready availability and ability to producestrong molds unaffected by moisture. Urea resins are most preferredbecause of their wide applicability and speed of cure.

The amount of moisture in the sand mix is important, as is wellunderstood in the art. In general the moisture content may vary from 1to 6% by weight on the resin, although a more preferred range is from 2to 5%. Dextrine or cereal products permit the use of greater amounts ofmoisture since they have a drying effect on the sand mix. Humectantssuch as ethylene glycol and glycerol act to hold the moisture content onexposure to air and prevent variations in moisture content.

From the above, it is apparent that the present method utilizes arelatively higher resin/ sand ratio than is conventional. Conventionalcore binder use of these resins is from 0.5 to 2% based on the amount ofthe sand. Thus the use of the method involves the molding of sand mixescontaining relatively larger proportions of resin and moisture. Theblowing of such sand mixes in blowing machines of the core-making typeis also a novel and preferred embodiment of the process of theinvention.

In general any refractory material of a suitable size and particle sizedistribution may be utilized in the casting method of this invention.Silica, various fire clays and mixtures thereof alone or with sand maybe utilized, desirably in the casting of higher melting metals andalloys. Ordinary molding sands, which are free of substantial amounts ofclay and other refractory binder substances should preferably be of theround or sub-angular grain type. Such sand is available in a wide rangeof particle sizes over the entire A. F. S. range containing particlesranging from about to 210 mesh or finer, U. S. Series. In general thecoarser sands favor higher baked strength, higher permeability, greaterhardness, and greater ease of blowing. The finer sands favor highergreen strength and better collapsibility. However, since the inventionis concerned with precision casting and the production of castings witha superior finish, the finer sands in the range of 60 to 150 A. F. S. orfiner will usually be required. Coarser sands can be utilized if thegreen molds are surface treated with slurries of very time refractorymaterials to produce a sooth finish. Sands of 80 to 120 A. F. S. willusually be satisfactory for most uses.

While the invention has been described with particular reference tocertain preferred embodiments thereof, it is possible to make variationsand modifications therein without departing from the spirit and scope ofthe invention as defined in the appended claims.

I claim:

ill

l. The process of precision casting of metals which com- I prisesshaping a wet sand molding mixture comprising fine molding sand, waterand a water-soluble urea-formaldehyde resin in an enclosure containing apattern means adapted to shape at least two of the inner, complementary,metal-contacting sand surfaces only and a removable drier supportadapted to shape the outer supporting surfaces only of a sand moldcomponent, removing said drier support and its adhering green sand moldcomponent from said enclosure, heat-hardening said green sand moldcomponent in contact with said drier support, assembling a plurality ofsaid heat-hardened mold components to form a complete, self-supportingsand mold, and casting 10 metal in said completed sand mold while it issupported by the shaped outer surfaces thereof.

2. The method of making self-supporting, resin-bonded molds for theprecision casting of metals which comprises packing a wet moldingmixture comprising a finely-divided refractory material and an aqueousdispersion of a water-dispersible, heat-hardenable binder into themolding cavity defined between a re-usable drier support adapted toshape the outer surfaces only of a mold and a forming member adapted toshape at least two of the inner,-complementary, metal-contactingsurfaces of said mold, heat-hardening the resulting green mold while incontact with said drier support, and separating the resultingheat-hardened mold from said drier support.

3. The method of making self-supporting, resin-bonded sand molds for theprecision casting of metals which comprises blowing a wet sand mixturecomprising molding sand and an aqueous solution of a water-solubleresinous binder into a molding cavity defined between a blower headadapted to shape at least about two of the inner, complementary,metal-contacting surfaces only of a sand mold and a reusable driersupport adapted to shape the outer surfaces only of said mold,heat-hardening the resulting green sand mold while supported in contactwith said drier support, and separating the resultant heathardened,self-supporting, resin-bonded sand mold from said drier support.

4. The method of making self-supporting, resin-bonded, multiple-cavitysand molds for the precision casting of metals which comprises blowing awet sand molding mixture comprising molding sand and an aqueous solutionof a water-soluble, thermosetting resinous binder into a plurality ofcomplementary portions of molding cavities defined between a blower headadapted to shape at least two of the inner, complementary,metal-contacting sand surfaces only of a sand mold component and a driersupport adapted to shape the outer sand surfaces only of said moldcomponent, said drier support also being adapted to form in the outersurfaces of said mold component planar supporting surfaces andreinforcing elements, heat-hardening the resultant green mold componentwhile in contact with said drier support, separating the resultantheat-hardened, resin-bonded sand mold component from said drier support,and assembling a pair of the so-formed sand mold components, each ofwhich has said plurality of complementary mold cavity portions, in faceto face relationship with one component turned with respect to the otherso that the complementary metal-contacting surfaces of adjacentlyassembled components are in cooperative face to face relationship toform a complete, multiple-cavity, self-supporting sand mold.

5. The method of making self-supporting, resin-bonded, multiple-cavity,multiple-mold sand mold assembly for the precision casting of metalswhich comprises forming green sand mold component parts by blowing a wetmolding mixture comprising fine molding sand and a watersolublethermosetting resinous binder selected from the group consisting of theintermediate, water-soluble condensation products of urea andformaldehyde and of phenol and formaldehyde into a plurality ofcomplementary portions of molding cavities defined between a blower headadapted to shape at least two of the interior, complementary,metal-contacting surfaces only of a sand mold and a drier supportadapted to shape the exterior surfaces only of said sand mold, saiddrier support also being adapted to form in exterior mold surfacesintegrally-molded planar supporting surfaces, reinforcing means, andpositioning and interlocking means, heat-hardening said sand moldcomponent parts while in contact with said drier support, separating theresulting heat-hardened sand mold components from said drier support,assembling a plurality of said mold components, each of which has saidplurality of complementary mold cavity portions, in face to facerelationship with one component turned 180 with re- 11 spect to theother so that the complementary metal-contacting surfaces of adjacen'tlyassembled components are in cooperative face to face relationship toform a multiplecavity sand mold, and interlocking a plurality of saidsand molds to form a multiple-cavity, multiple-mold sand mold assembly.

6. The method of making self-supporting, resin-bonded molds for theprecision casting of metals which comprises packing a Wet moldingmixture comprising a finelydivided refractory material and an aqueousdispersion of awater dispersible, heat-hardenable binder into themolding cavity defined between a re-usable drier support adapted toshape the outer surfaces only of a mold and a forming member adapted toshape at least two of the inner, complementary metal-contacting surfacesof said mold, removing said forming member, heat-hardening the resultinggreen mold While in contact with said drier support, and separating theresulting heat-hardened mold from said drier support.

References Cited in the'file of this patent UNITED STATES PATENTS2,368,719 Miller Feb. 6, 1945 ture, by Tidula.

. 12 2,435,858 .Whitehead Feb. 10, 1948 2,445,141 Hardy July 13, 19482,691,196 Banister Oct. 12, 1954 2,720,687 Shaw Oct. 18, 1955 52,724,158 Davis et al Nov. 22, 1955 FOREIGN PATENTS 174,696 GreatBritain Jan. 25, 1922 832,634 Germany Mar. 3, 1952 10 683,239 GreatBritain Nov. 26, 1952 OTHER REFERENCES Modern Metals, October 1950,pages 22-24.

The Foundry, October 1950, pages 162, 164, 168.

American Foundryinan, August 1952, pages 4246, vol. 22, No. 2. (Page 44relied on.)

The Foundry, November 1952, pages 102-107, 282-290. Top of page 284pertinent.

Shell-Molding Patents and Recent Technical Litera- Snpplement No. 1PB-106640 S. Published April 1953 by Office of Technical Services, U. S.Dept. of Commerce of Washington, D. C. 12 pages. Pages 3 and 4 ofinterest.

